I'am using a level shifter IC to convert 3.3v TX to 2.8RX of a SIM900 (GSM module) It works great. But, I also want to use it on the PWR_PIN that switch on the SIM900. (because It have unused pins)
The SIM900 Datasheet said :
I have wired the level sifter like this : TP1 is on the GSM. TP2 is on the ATMEGA.
The level sifter is http://www.ti.com/product/sn74avc4t245?qgpn=sn74avc4t245
Why if I pull TP2 to low, then TP1 dont goes low. But, if I take a wire and set TP1 to GND, the SIM900 switch on, and then if I pull TP2 to low from the ATMEGA it shutdown properly the SIM900 (so the level shifter works like it should). Can you help me to undersand why ? When I put TP1 to GND with a wire, the power current increase to 0.1 A (idle 0.05 A), why ?
Big thanks to you